Investigation on the Effect of Accumulated Charge-Induced Degradation on Multilayer Photovoltaic Insulating Backsheets Based on Atomic Force Microscopy

Abstract

As a clean and renewable energy, solar energy has drawn people’s attention to mitigate the energy crisis around the world. A solar photovoltaic (PV) system is a reliable way to collect solar energy whose service lifetime is usually shorter than the designed time because of accumulated charge-induced degradation caused by electrical aging. With the rapid development of PV systems, the traditional polyethylene terephthalate (PET) backsheet cannot meet the requirements of insulation and package for the advanced solar energy system. In this context, two different backsheet materials, namely, KPK (polyvinylidene fluoride, PET, polyvinylidene fluoride) and TPT (polyvinyl fluoride, PET, polyvinyl fluoride), were selected to explore accumulated charge-induced degradation caused by partial discharge (PD) and corona discharge. In this paper, the backsheets were electrically stressed for 30, 60, and 120 min by PD and electrically stressed for 10 min by corona discharge. The accumulation and transportation of charges were investigated by phase-resolved partial discharge (PRPD) and surface potential decay (SPD). At the same time, the topography of KPK and TPT determined using atomic force microscopy after PD activity was also investigated. The explorations of PD activity showed that KPK and TPT have a similar PD resistance, but their SPD were entirely different after corona discharge. The research works in this paper provide an important path to investigate the aging process of insulating polymers and evaluate the lifetime of insulating backsheets of PV modules, as well as a guidance to improve the testing standards for the PV system.

Investigation of the Potential-Induced Aging Phenomenon of an Insulating Encapsulant for a Photovoltaic Module: From Electrical to Chemical Properties

“…As shown in Figure , it is obvious that PD events on all of the samples occur at a phase angle of 0–90° and 180–270°. The drop off in the electric field at the defects inside these samples after the occurrence of the first discharge event, induced by the opposite field polarity between the field resulting from the accumulation of free charge and the applied field, is a large contributor to the PD phenomenon that occurred at a specific phase angle . The PRPDs evidently appear in two regions marked in red and black.…”

“…The drop off in the electric field at the defects inside these samples after the occurrence of the first discharge event, induced by the opposite field polarity between the field resulting from the accumulation of free charge and the applied field, is a large contributor to the PD phenomenon that occurred at a specific phase angle. 15 The PRPDs evidently appear in two regions marked in red and black. The red parts are considered as regions where the PD activities frequently occur, whereas the black parts indicate those regions where the PD events infrequently occur.…”

“…An initial seed electron can lead to an electron avalanche, which is a critical precondition for the occurrence of a PD activity. ,− The number of initial seed electrons has an effect on the statistical parameters of the PD event, which include the delay of the initial partial discharge, frequency of the occurrence of PD activity, and the PRPD . The main generation mechanism of the initial seed electrons is the surface emission induced by the applied field .…”

“…15,17−23 The number of initial seed electrons has an effect on the statistical parameters of the PD event, which include the delay of the initial partial discharge, frequency of the occurrence of PD activity, and the PRPD. 15 The main generation mechanism of the initial seed electrons is the surface emission induced by the applied field. 21 The generation rate of a seed electron is mainly related to the applied voltage (applied field), material conductivity and permittivity, etc.…”

Lifetime Evaluation of Photovoltaic Polymeric Backsheets under Ultraviolet Radiation: From Chemical Properties to Mechanical Modeling

“…With the degradation of polymeric materials, the thickness of the polymer decreases continuously, which can result in the production of pits. The accumulation of charges in these pits can effectively improve the probability of initial electrons, which can easily generate PD and lead to stronger discharge. − Figure c shows the surface topography of PET after UV radiation and PD stress. Some burn marks exist on the surface of PET films, which may be related to the bombardment from high-energy ions and high temperature generated by discharge during PD.…”